1. Field of the Invention
The present invention relates to a deformable intraocular contact lens to correct vision problems, which lens is inserted into the eye anterior to the natural lens and has a functional design which minimizes cutting or stretching of the cornea to do so.
2. Description of the Related Art
Doctors trained in ophthalmology routinely surgically extract cataract-impaired lenses from patients' eyes and subsequently implant artificial lenses to prevent blindness. The artificial lens is typically manufactured from polymethylmethacrylate (PMMA), an acrylic plastic. PMMA is a preferred material because it is biologically compatible with the tissue of the eye, and it does not degrade over time.
Over the last 50 years, the success rate for implanting these intraocular lenses has improved to the point that surgeons now want to implant intraocular contact lenses anterior to the natural lenses to correct common vision problems, such as myopia (near-sightedness), hypermetropia (far-sightedness), and astigmatism (aberration in the convexity of the optic lens or cornea). However, using an intraocular lens for vision correction is currently problematic. In order to insert an intraocular lens, an incision of approximately 10 mm is made through the cornea or sclera. The new lens is passed through the incision into the anterior chamber of the eye. The inserted lens is then positioned over the pupil and anchored either anteriorly to or posteriorly from the iris. Unfortunately, the making of the incision causes astigmatism of the cornea.
Experience from cataract surgeries shows that the astigmatism will be reduced if a smaller incision is made. It follows that if the lens could be manipulated through a smaller incision, it will reduce the severity of the astigmatism. The optical portion of the intraocular lens, though, must have a diameter of at least approximately 6 mm in order to properly cover the pupil. So, the only way to pass a lens through a smaller incision is to first fold the lens into a U-shape or roll it so that the opposite edges are overlapping. However, currently designed PMMA lenses are rigid and too brittle to be rolled or folded. While it is known that a material which is rigid at a given thickness may be flexible at a lesser thickness, the maximum material thickness under which PMMA is flexible is approximately 0.25 mm. This thickness is too thin for use in a conventional contact lens because of the lens' optics requirements.
A lens has a convex lenticular surface into which incident light passes. The lens also has a posterior surface, opposite the lenticular surface, from which the refracted light exits. The posterior surface may be convex, planar or concave. The power of the lens is determined by the curvature of the lenticular and posterior surfaces. Because the optical portion of the contact lens is approximately 6 mm wide and the thickest portion is at the center of the lens, a conventional lens having a maximum thickness of under 0.25 mm at its center in order to be rolled cannot possess the requisite curvature to be optically useful.
Alternative lens materials are also currently used for the replacements of the natural lenses of cataract patients. One such alternative lens material is an acrylic that has a lower molecular weight than PMMA. This lower-weight acrylic lens is softer than PMMA so it can be folded in a U-shape. However, if not handled very carefully, the lower-weight acrylic will crease, rendering it unusable. In addition, the material is soft enough to adhere to itself if it is rolled or folded far enough to allow overlapping.
Another alternative lens material is silicone, the same material that is used in breast implants. The silicone collects protein in some patients, giving a yellow appearance and reducing the passage of light. The protein can become so dense as to create the appearance of a secondary cataract, significantly reducing the patient's ability to see. This is usually a lesser concern for cataract patient, when compared to the blindness which would result from the cataract. Also, most cataract patients tend to be elderly so the protein build-up might not advance too far during their lifetimes. For some cataract patients, though, the protein build-up necessitates that the silicone lens be removed and replaced. Because of the problems associated with protein build-up, silicone cannot be used to make long-term intraocular contact lenses for implantation into younger persons.
Two inventions for a deformable intraocular lens are set forth in U.S. Pat. No. 4,573,998 issued March 1986, to Mazzocco; and U.S. Pat. No. 5,522,890 issued June 1996, to Nakajima et al. These inventions employ a lens made of a molded elastic material. They do not suggest the use of PMMA.
Other inventions generally related to the art of optical lenses include: U.S. Pat. No. 4,254,509 issued March 1981, to Tennant (Accommodating Intraocular Implant); U.S. Pat. No. 4,585,456 issued April 1986, to Blackmore (Corrective Lens for the Natural Lens of the Eye); U.S. Pat. No. 4,655,775 issued April 1987, to Clasby (Intraocular Lens with Ridges); U.S. Pat. No. 4,769,035 issued September 1988, to Kelman (Artificial Lens and the Method for Implanting Such Lens); U.S. Pat. No. 4,795,462 issued January 1989, to Grendahl (Cylindrically Segmented Zone of Focus Artificial Lens); U.S. Pat. No. 4,816,032 issued March 1989, to Hetland (Arrangement in an Intraocular Anterior Chamber Lens); U.S. Pat. No. 4,950,290 issued August 1990, to Kamerling (Posterior Chamber Intraocular Lens); U.S. Pat. No. 4,994,080 issued February 1991, to Shepard (Optical Lens Having at Least One Stenopaeic Opening Located in the Central Area Thereof); U.S. Pat. No. 5,076,684 issued December 1991, to Simpson et al. (Multi-Focal Diffractive Ophthalmic Lenses); U.S. Pat. No. 5,098,444 issued March 1992, to Feaster (Epiphakic Intraocular Lens and Process of Implantation); U.S. Pat. No. 5,166,711 issued November 1992, to Portney (Multifocal Ophthalmic Lens); U.S. Pat. No. 5,229,797 issued July 1993, to Futhey et al. (Multifocal Diffractive Ophthalmic Lenses); U.S. Pat. No. 5,258,025 issued November 1993, to Fedorov et al. (Corrective Intraocular Lens); U.S. Pat. No. 5,480,428 issued January 1996, to Fedorov et al. (Corrective Intraocular Lens). None of these inventions solves the above-disclosed problems associated with currently known deformable intraocular lenses.
Thus, a need exists for a deformable intraocular contact lens which requires a minimal incision through the cornea, but does not possess the drawbacks associated with the currently known, alternative lens materials. None of the above inventions and patents, taken either singularly or in combination, is seen to describe such a lens as is achieved by the instant invention as claimed.